This invention relates generally to medical devices for delivering a biologically active material to a desired location within the body of a patient. More particularly, the invention is directed to medical devices having a sponge coating comprising a non-hydrogel polymer and a plurality of voids therein, optionally formed by eluting a particulate material from the polymer. The sponge coating is capable of being loaded with a drug, e.g. infusing or placing the drug into the voids, for release into the body upon expansion of the coated portion of the medical device.
For certain diseases which are localized to a particular part of the body, the systemic administration of drugs for the treatment of these diseases may not be preferred because of the inefficiencies associated with the indirect delivery of the drugs to the afflicted area. Instead, it may be preferred that the drug be directly applied to the diseased tissue. However, such localized delivery of drugs to the walls of lumens, such as blood vessels and ducts, can be problematic since lumens are involved in the transport of body fluids, which tend to carry the drug away from the afflicted area. Thus, there is a need for devices and methods for the localized delivery of drugs to afflicted tissue, especially body lumens.
A number of methods for delivering drugs to body lumens or vessels involve the use of catheters having expandable portions, such as a balloon, disposed on the catheter. For instance, U.S. Pat. No. 5,304,121 to Sahatjian, PCT application WO 95/03083 to Sahatjian et al. and U.S. Pat. No. 5,120,322 to Davis et al. describe medical devices in which the exterior surface of the device is coated with a swellable hydrogel polymer. A solution of a drug to be delivered to the afflicted tissue is incorporated into the hydrogel. The drug is held within the matrix of the hydrogel. In the case where the medical device is a balloon catheter, the drug is delivered by inserting the catheter into the body lumen and expanding the coated balloon against the afflicted tissue of the lumen to force the drug from the hydrogel into the tissue.
However, these hydrogel coated devices have certain disadvantages. In particular, since the hydrogels are waterbased, only hydrophilic drugs can be effectively incorporated into the hydrogels. Therefore, a number of useful hydrophobic biologically active materials or drugs, such as dexamethasone, cannot be suitably embedded into these hydrogels. Hence, there is a need for a coating for a medical device which can effectively incorporate such hydrophobic drugs in relatively large quantities.
Also, the application of the hydrogel coating to the balloon usually involves multiple steps because most balloon materials are hydrophobic so that a hydrogel usually has poor adhesion to the balloon surface. Another disadvantage with hydrogels is that the hydrogels will tend to be tacky or sticky when they are not fully hydrated. When a hydrogel is not in its fully hydrated state, it can stick to the surface of the packaging material or protection sheath for the coated device and make the insertion or implantation of the device difficult.
Moreover, even when prostheses having a drug containing coating are implanted into the body, it is desirable to apply a dose of the drug to the implantation site in addition to that contained in the coating. Hence, there is a need for a device which can deliver a prosthesis as well as a dose of the drug to the implantation site.
These and other objectives are accomplished by the present invention. To achieve the aforementioned objectives, we have invented a medical device and a method for making and using such device for the localized delivery of biologically active materials as well as implanted prostheses to a patient.
The medical devices of the invention comprise an expandable portion which is covered with a sponge coating for release of at least one biologically active material. The sponge coating is made of a non-hydrogel polymer having a plurality of voids. The void space of the sponge coating is greater than about 60% of the volume of the sponge coating. The device can further include means for infusing the biologically active material or drug into the voids.
In an embodiment of the invention, the device is a catheter having an expandable portion which can be inflated or expanded by inflation pressure to fill the cross-section of the body lumen and engage the tissue of the body lumen. Upon expansion, the biologically active material, which has been placed into the voids of the sponge coating, is released into the body. The catheter can also be capable of performing an angioplasty procedure at pressures of greater than 6 atm and delivering an implantable prosthesis such as a stent.
In another embodiment, the infusion means of the catheter can further comprise an inflation lumen connected to a balloon with pores. The balloon is filled with a biologically active material. When the balloon is inflated, the biologically active material infuses into the voids of the sponge coat and can be released into the body lumen.
In yet another embodiment of the present invention, a catheter has an expandable portion which comprises a reservoir defined by a porous membrane. The porous membrane or film is used to separate the sponge coating and the reservoir. The reservoir can be connected to a reservoir lumen, thereby allowing the reservoir to be filled with a biologically active material. Disposed about the porous membrane of the reservoir is a sponge coat comprising a non-hydrogel polymer having a plurality of voids formed by eluting a particulate material from the polymer. Elution of the particulate material means that such material becomes dissolved or suspended in a surrounding solvent or fluid. The catheter can further include a balloon disposed within the reservoir, wherein the balloon is connected to an inflation lumen. When the balloon is expanded the biologically active material of the reservoir is expelled or xe2x80x9csqueezed outxe2x80x9d through the porous membrane and infused into the voids of the sponge coat. Upon further expansion the biologically active material is released from the sponge coating into the body lumen.
Furthermore, in another embodiment of the invention the medical device, which is coated with a sponge coating is an expandable stent. The stent can be a self-expanding or balloon expandable stent.
The devices of the present invention are prepared by applying a sponge coating composition to a surface of an expandable portion of a device. The sponge coating composition comprises a non-hydrogel polymer dissolved in a solvent and an elutable particulate material. After the sponge coating composition is cured, it is exposed to a solvent, e.g. water, which causes the particulate material to elute from the polymer leaving a sponge coating having a plurality of voids therein. The sponge coating is then exposed to a biologically active material to load the sponge coating with such material. Such material may be loaded into the coating by diffusion or other means.